The earliest predictor of the development of type 2 diabetes is low insulin sensitivity in skeletal muscle, but it is important to recognize that this is not a distinct abnormality but rather part of the wide range expressed in the population. Those people in whom diabetes will develop simply have insulin sensitivity, mainly in the lowest population quartile (29). In prediabetic individuals, raised plasma insulin levels compensate and allow normal plasma glucose control. However, because the process of de novo lipogenesis is stimulated by higher insulin levels (38), the scene is set for hepatic fat accumulation. Excess fat deposition in the liver is present before the onset of classical type 2 diabetes (43,74–76), and in established type 2 diabetes, liver fat is supranormal (20). When ultrasound rather than magnetic resonance imaging is used, only more-severe degrees of steatosis are detected, and the prevalence of fatty liver is underestimated, with estimates of 70% of people with type 2 diabetes as having a fatty liver (76). Nonetheless, the prognostic power of merely the presence of a fatty liver is impressive of predicting the onset of type 2 diabetes. A large study of individuals with normal glucose tolerance at baseline showed a very low 8-year incidence of type 2 diabetes if fatty liver had been excluded at baseline, whereas if present, the hazard ratio for diabetes was 5.5 (range 3.6–8.5) (74). In support of this finding, a temporal progression from weight gain to raised liver enzyme levels and onward to hypertriglyceridemia and then glucose intolerance has been demonstrated (77).
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.